1. Field of the Invention
The present invention relates to a process for preparing hydrogen gas from the reduction of water, and also relates to a process for determining the ratio of the masses between hydrogen isotopes in the obtained hydrogen gas.
2. Prior Art
Many elements occur in nature as mixtures of isotopes having the same atomic numbers but different mass numbers. One type of such isotopes is a radioactive isotope which is characterized by spontaneous transformation of nucleide into one or more different nucleides. The radioactive isotope of the element, such as .sup.14 C, .sup.126 I, or .sup.3 H has been used as an isotopic tracer or an isotopic indicator of chemical, biological, and physical processes, and also used in a method of determining the age of geological, archeological objects, or the like. The other type of isotopes is a stable isotope which is characterized by its stable physical properties. The stable isotope of the element has been used as a tracer especially in the field of medical chemistry, environmental monitoring or the like methods so as to avoid side effects of the radiation.
In the case of hydrogen, for example, there are three isotopes existing in nature. First type is an ordinary hydrogen, .sup.1 H, nucleus thereof consists of a single proton and is the most abundant of the three isotopes of hydrogen. Second type is deuterium, .sup.2 H, which is called heavy hydrogen, consisting of one proton and one neutron, and also deuterium is often denoted by a symbol D. It is noted that deuterium naturally occurs only in about 1 of every 5000 atoms of naturally occurring hydrogen. Another isotope of hydrogen, .sup.3 H, is called tritium (symbol T). It is radioactive, and because of its relatively short half-life of 12.3 years, only 1-10 of every 10.sup.18 atoms of naturally occurring hydrogen is tritium.
In general, the mass ratio of stable isotopes of hydrogen, i.e., the ratio of the masses between ordinary hydrogen elements and deuterium elements in a sample of water can be estimated by the method comprising the steps of reduction of water molecules to gasify the whole mass of hydrogen in the sample, and supplying the obtained hydrogen gas into a stable-isotope mass spectrometer for determining the masses of isotopes of the hydrogen gas. The mass spectrometer is a well-known instrument that is able to determine very precisely the masses of ions formed from molecules when they are bombarded by electrons. It is a valuable analytic tool in chemistry and biochemistry.
Conventionally, there are two methods for preparing hydrogen gas from water i.e., a depleted uranium method (uranium reduction method, see Bigeleisen et al., Anal. Chem. 24, 1356-1357, 1952) and a zinc reduction method (see Colemch et al, Anal. Chem. 54, 993-995. The depleted uranium method comprises the steps of: passing water through a unit having depleted uranium at a preferable temperature (700.degree. C.) to generate hydrogen gas by the reduction of water; and recovering the hydrogen gas by means of the tabular pump. On the other hand, the zinc reduction method comprises the steps of: reacting water with zinc at the high temperatures (400.degree.-450.degree. C.) so as to generate hydrogen gas. In this method, the reduction of water proceeds by the following reaction: EQU H.sub.2 O+Zn.fwdarw.H.sub.2 +ZnO
According to the conventional methods described above, hydrogen elements in the sample can be gasified. Consequently, the masses of hydrogen isotopes can be determined by supplying the obtained gas into the mass spectrometer.
However, the conventional methods described above have some problems. In the case of the uranium reduction method, for example, (i) depleted uranium is hard to obtain; (ii) a step of recovering the generated gas is time consuming; (iii) it is difficult to determine the masses of hydrogen isotopes when several different water samples are serially passed through one unit of depleted uranium. In the case of the zinc reduction method, on the other had, it is difficult to perform the reduction of water molecules in the sample perfectly.
Therefore, there has long been felt a need for a simple process of preparing hydrogen gas which may be performed quickly to determine the masses of hydrogen isotopes in the hydrogen gas with a high accuracy of measurement.